The requirements imposed on a modern internal combustion engine become ever greater with the view of reducing the consumed fuel and the discharged exhaust gases and the toxic substances contained therein. This is the same as the objective of improving the combustion in the combustion chamber of the engine and especially to obtain the most complete combustion possible. To reduce the nitrogen oxide, the exhaust gas discharged from the combustion chamber is fed back into the intake manifold and therefore into the combustion chamber for further or renewed combustion.
This can be carried out by means of an external exhaust-gas return wherein a controllable exhaust-gas feedback valve is introduced into an exhaust-gas return line. With this feedback valve, the quantity of the exhaust gas to be fed back can be adjusted. Alternatively, or in addition, it is possible to provide an internal exhaust-gas return wherein an inlet valve of the engine is controlled in such a manner that it is opened at least for a short time duration during the discharge phase of the engine. During this time duration, the exhaust gas from the combustion chamber can reach the intake manifold and this defines an exhaust-gas feedback.
A further measure for improving the operation of the engine comprises precisely detecting the sequence of the combustion, which takes place in the combustion chamber of the engine, in order to be then able to consider the sequence especially as to the metering of fuel into the combustion chamber. One possibility to achieve this comprises forming a model of the engine and especially of the sequence of the combustion in the combustion chamber. As to a model, a type of engine observer is understood in this case. In this way, it can be achieved that the conditions present in the combustion chamber can be taken or derived from the model at each time point. The operating variables of the engine such as the fuel mass to be metered can be optimally determined and adjusted in dependence upon these conditions.